1. Field of the Invention
The present invention relates to novel isocyanate-terminated polyether-based polymer prepolymer compositions which are especially useful in the preparation of high resiliency flexible polyurethane foams and moisture-cured adhesives. More particularly, this invention relates to an improved process for preparing isocyanate-terminated prepolymers whereby one or more ethylenically unsaturated monomers are polymerized in the presence of an isocyanate-terminated polyether-based prepolymer to form a composition comprising a stable dispersion of the polymer in the prepolymer in admixture with a proportion of polymer grafted onto the isocyanate-terminated prepolymer.
2. Description of the Prior Art
Polyurethanes constitute a broad class of polymeric materials having a wide range of physical characteristics. The polymers are produced through the interaction of a polyfunctional isocyanate with a polyfunctional chemical compound having an active hydrogen in its structure, such as a polyester or polyether or mixtures of two or more of such materials. The materials conventionally used contain two or more hydroxyl groups and are thus generally termed polyols. In the preparation of flexible polyurethane foams, it is sometimes advantageous to employ a method known as the quasi-prepolymer method wherein a portion of the polyether polyol component is reacted with an excess of isocyanate. Then in a second step the quasi-prepolymer is mixed with the balance of the polyether polyol along with a blowing agent and catalyst to produce the polyurethane foam. Despite the variety of physical and chemical properties obtainable by proper selection of the polyisocyanate and the polyol, as well as the conditions under which the reaction is carried out, there are definite limitations in the properties obtained in the resulting polyurethane composition.
It is known in the art that the addition of a high molecular weight polymer to polyurethane composition will improve certain of the physical properties of the resulting polyurethane composition. There have been many efforts with respect to incorporating polymers into such polyurethane compositions. See for example, U.S. Pat. No. 3,383,351 which discloses the in situ polymerization of an ethylenically unsaturated monomer in the presence of the polyol component of a polyurethane composition. These compositions are known in the art as polymer/polyols or graft polymers. For other examples of the state of the art with respect to such products, see U.S. Pat. 3,304,273; 3,652,639; 3,405,162; 3,546,321 and 3,110,695.
Despite the great amount of art relating to the incorporation of polymer/polyols into polyurethane compositions, there still remains several problems not solved by the compositions known in the art. There is still a need for polyurethane foam compositions which will result in foams with an improved tensile and tear strength, which have a uniform cell structure and which upon curing, do not show an appreciable shrinkage. None of the polyurethane formulations of the prior art which employ the polymer polyols is completely satisfactory for these purposes.
Accordingly, it is an object of this invention to provide an isocyanate-terminated polyether-based prepolymer composition into which is incorporated one or more polymerized ethylenically unsaturated monomers. The resulting isocyanate-terminated polyether-based polymer prepolymer composition can be thereafter reacted with additional polyol to form a flexible polyurethane foam having improved physical properties and without appreciable shrinkage of the polyurethane reaction product.
It is also an object of this invention to provide isocyanate-terminated polymer prepolymer compositions which have exceptional stability and do not exhibit large viscosity increases upon prolonged storage.
A further object of the invention is to provide a novel method of forming polyurethanes utilizing high molecular weight polymer polyisocyanates as one of the components in the polyurethane formulation. Such products show special utility in the preparation of adhesives, coatings, elastomers, etc.
The advantages and other objects of this invention will become apparent to those skilled in the art in view of the aforementioned background, the following discussion, and the accompanying examples.